Polymers having narrow molecular weight distribution and specific molecular weight, polymers having a functional group introduced at the terminal and block polymers having different segments bonded to each other exhibit various useful properties, so that they are very important from not only the academic viewpoint but also the industrial viewpoint.
It is generally well known that in the production of polymers having such specific structures, living polymerization wherein neither termination reaction nor chain transfer reaction substantially takes place during the polymerization is effective.
However, if the polymerization is carried out under usual conditions using a Ziegler catalyst or a metallocene catalyst that is generally used as an olefin polymerization catalyst to produce polymers having the above specific structures, chain transfer reactions of the glowing polymer chains frequently take place, and it is very difficult to produce olefin polymers by living polymerization. For example, it has been made clear by analyses of molecular weight distribution, composition distribution, etc. that when a block copolymer is intended to be synthesized using a known catalyst system, a mixture of homopolymer and random copolymer is produced (Boor, “Ziegler-Natta Catalyst and Polymerization”, Academic Press Co., 1979).
Under such circumstances, some researches of living polymerization of olefins have been reported.
For example, living polymerization of propylene using a specific vanadium catalyst has been reported by Doi, et al. (Macromolecules, vol. 19, p. 2896, 1986). In this process, however, an extremely low polymerization temperature such as a temperature of −78° C. to −40° C. is necessary, and the polymerization activity is several tens g-polymer/mmol-M-h and is not commercially satisfactory. Further, the polymer type which can be synthesized is restricted to polypropylene or a propylene/ethylene copolymer having a low ethylene content (not more than 50% by mol), and it is difficult to produce commercially useful polyethylene and ethylene copolymers by living polymerization. Moreover, there is a problem of low stereoregularity (racemic diad: not more than 0.8) of the resulting polypropylene, and hence this process is industrially insufficient.
Brookhart, et al. and McConvill, et al. have reported living polymerization of higher α-olefins such as propylene and 1-hexene with specific nickel complex or titanium complex (Journal of American Chemical Society, vol. 118, p. 11664, 1996, Journal of American Chemical Society, vol. 118, p. 10008, 1996). Also in this process, low-temperature polymerization at a temperature of not higher than 0° C. is necessary in many cases, and the resulting polymer has an atactic structure having no stereoregularity. Moreover, it is difficult to produce polyethylene or an ethylene polymer by living polymerization using the nickel complex or the titanium complex.
Soga, Shiono, et al. have studied living polymerization of propylene using a metallocene catalyst, but in this process, an extremely low temperature such as a temperature of −78° C. to −60° C. is necessary, and the levels of polymerization activity and molecular weight of the resulting polymer are low (Macromolecule, vol. 31, p. 3184, 1998, Macromolecule Rapid Communication, vol. 20, p. 637, 1999).
As a synthesis of polyethylene by living polymerization, that is generally said be difficult, Nakamura, et al. have reported a process of using a niobium or tantalum complex, and Yasuda, et al. have reported a process of using a samarium complex. In these processes, however, there are defects that the activity is low, the molecular weight of the resulting polyethylene is limited to about 100,000, and copolymerization of comonomers other than ethylene is infeasible (Journal of American Chemical Society, vol. 115, p. 10990, 1993).
As a synthesis of a block polymer having different segments bonded to each other, a process of using a specific metallocene catalyst has been reported (International Patent Publication WO91/12285, WO94/21700). In this process, however, the activity is low, and low-temperature polymerization (−10° C. to 0° C.) is essential Moreover, it is described that the blocking efficiency is decreased to less than 10% by increasing the polymerization temperature to 10° C. On this account, production of a block copolymer at an industrially usually used polymerization temperature (50° C. to 75° C.) is impossible. Also in case of low-temperature polymerization, the molecular weight distribution (Mw/Mn), that is an indication of living polymerizability, of the block copolymer is not less than 1.35 and is not narrow, so that this polymerization is not living polymerization sufficiently controlled. Therefore, most of the products contain large amounts of non-block polymers as by-products, and fractionation to remove the unnecessary polymers is essential as a post treatment. Thus, there are many industrial restrictions.
Accordingly, development of a process wherein living polymerization of olefins can be carried out at an industrially available high temperature with high polymerization activity is of industrially very great value.
Under such circumstances, the present applicant has found, as novel olefin polymerization catalysts, transition metal compounds having a salicylaldimine ligand, and has also found that when a transition metal compound having a specific structure selected from the transition metal compounds having a salicylaldimine ligand is used, living polymerization proceeds at an industrially available high temperature with activity extremely higher than that of hitherto known living polymerization, and production of polyolefins having high molecular weight and narrow molecular weight distribution and polyolefins or block copolymers having functional groups quantitatively introduced at the terminals is feasible. Based on the finding, the present invention has been accomplished. The present applicant has furthermore found a process for efficiently producing such polymers, and accomplished the present invention.
It is an object of the invention to provide olefin polymers exhibiting various useful properties, such as a polymer having a narrow molecular weight distribution and a specific molecular weight, a polymer having a functional group introduced at the terminal and a block polymer having different segments bonded to each other. It is another object of the invention to provide processes for preparing these olefin polymers. It is a further object of the invention to provide processes for efficiently preparing such polymers.